Method and Device for Granulating Plastics and/or Polymers

ABSTRACT

The present invention relates to a method for the pelletization of plastics and/or polymers, wherein a melt coming from a melt generator is supplied via a diverter valve having different operating positions to a plurality of pelletizing heads through which the melt is pelletized. The invention furthermore relates to a pelletizing apparatus for the pelletization of plastics and/or polymers having a diverter valve which has at least one melt generator connection, at least two pelletizer connections as well as a switching gate for selectively connecting the melt generator connection to at least one of the pelletizer connections, with a respective pelletizing head being connected to the at least two pelletizer connections and a melt generator having a variable melt volume flow being connected to the melt generator connection. Finally, the invention also relates to a diverter valve for such a pelletizing apparatus having a melt generator connection, a pelletizer connection as well as a melt passage for the connection of the melt generator connection to the pelletizer connection. The present invention therefore starts from the idea of using a plurality of pelletizing heads with different passage capacities and of hereby enlarging the throughput window to be able to work largely continuously without intermediate interruptions and to shorten unavoidable start-up processes by switching in pelletizing heads having small throughput capacities or to minimize them with respect to the start-up products which occur. In accordance with an aspect of the present invention, a plurality of pelletizing heads having different throughput capacities are used sequentially for the start-up of the pelletizing process, with the melt first being supplied to a first pelletizing head having a smaller throughput capacity and then the melt volume flow being increased and the diverter valve being switched over such that the melt is diverted by the diverter valve to a second pelletizing head having a larger throughput capacity. The time and thus the amount of the start-up product until the melt generator reaches the lower throughput limit of the pelletizing head and the pelletizing process can be started are cut by the use of initially one pelletizing head having a throughput capacity which is as low as possible. No further start-up product is incurred from the start onwards of the pelletizing process at the lower throughput limit of the said first pelletizing head. The melt volume flow is increased quantitatively for so long until the diverter valve can be switched to the second pelletizing head having the larger throughput capacity with no start-up product being incurred during this time period. Moreover, the throughput window is enlarged in total so that the number of unavoidable start-up procedures with start-up product arising therein is reduced since it is possible, on a ramping down of the melting performance below the lower throughput limit of the larger pelletizing head which may become necessary for various reasons, to switch back to the first pelletizing head.

A method and an apparatus for the pelletization of plastics and/orpolymers The present invention relates to a method for the pelletizationof plastics and/or polymers, wherein a melt coming from a melt generatoris supplied via a diverter valve having different operating positions toa plurality of pelletizing heads through which the melt is pelletized.The invention furthermore relates to a pelletizing apparatus for thepelletization of plastics and/or polymers having a diverter valve whichhas at least one melt generator connection, at least two pelletizerconnections as well as a switching gate for selectively connecting themelt generator connection to at least one of the pelletizer connections,with a respective pelletizing head being connected to the at least twopelletizer connections and a melt generator having a variable meltvolume flow being connected to the melt generator connection. Finally,the invention also relates to a diverter valve for such a pelletizingapparatus having a melt generator connection, a pelletizer connection aswell as a melt passage for the connection of the melt generatorconnection to the pelletizer connection.

As a rule, diverter valves via which the pelletizer is connected to themelt generator are used for the start-up of pelletizer devices. This inparticular applies to complex production processes whose start-upprocedure is difficult as well as to applications in which uniformpellets should be generated as rapidly as possible. Diverter valves ofthis type are described, for example, in DE 102 34 228 A1; DE 38 15 897C2 or EP 0 698 461 B1. These diverter valves comprise, in the meltpassage which connects the inlet opening of the valve at the meltgenerator connection to the outlet opening at the pelletizer connection,a diverter gate which interconnects the connection of the melt generatorconnection to the pelletizer connection in the production position,whereas it keeps the melt flow away from the outlet opening at thepelletizer connection in its start-up position, i.e. it blocks it anddiverts the melt loss so that the melt flow entering at the meltgenerator connection does not move to the pelletizer connection, butinstead exits at a bypass opening of the valve and as a rule simplyflows onto the floor. If the pelletizer device has started up so thatall the units are working with the desired operating parameters and themelt flow has reached the desired quality, the diverter gate is switchedover to its production position so that the melt flow in the divertervalve. flows to its pelletizer connection and is then processed topellets by the pelletizer connected there.

The start-up phase of a production process can admittedly be effectedper se in a satisfactory manner using such known diverter valves;however, problems occur on the changing from one production process to asecond production process, for example on a change of the polymer/fillermixture, on a change of the pellet geometry, on a changeover to changedthroughput demands, on a change in the color of the pellets or also onscheduled or unscheduled production interruptions e.g. for repairs tothe nozzle plate. The problem which results in this process is that thetotal diverter valve, including the melt passage in the interior of thevalve, has to be cleaned completely before the plant can be started upagain. Without such a cleaning, contaminations of long duration wouldoccur, for example on the changeover from colored pellets to whitepellets. Conventional diverter valves have to be dismantled for cleaningas a rule, whereby the production process is interrupted for a longerduration. Moreover, subsequent to the cleaning, the fitting time has tobe taken into account which is needed, for example, for the heating ofthe diverter gate to operating temperature.

The possible alternative of having two separate diverter valvesavailable for such changes between two production processes is notacceptable for a number of operators of such plant. On the one hand, thecosts for two complete diverter valves are incurred. Apart from this,time delays also occur on the use of two separate diverter valves, e.g.due to the ramping up of the new diverter valve to operatingtemperature.

Furthermore, DE 696 21 101 T2 describes the possibility of viscositychange within a compounding process with subsequent pelletization in acorresponding large-production plant having a performance of at least1000 kg/h. Two pelletizer heads are connected to the valve connecteddownstream of the melt generator so that highly viscose material can begiven to the one pelletizing head and low-viscose material can be givento the other pelletizing head by switching over the valve. The problemsof the start-up losses are, however, not solved in this process; it israther the case that material not yet pelletizable should be dischargedvia a bypass opening in a manner known per se up to the reaching of therespective operating point. Furthermore, a pelletizing apparatus isdescribed in DE 197 54 863 C2 in which two pelletizing heads areconnected to a ⅓ valve so that, on a color change from black material towhite material or vice versa, the one or the other pelletizing head canselectively be selected. To so-to-say flush out color contaminations ona color change in this process, a central bypass outlet is provided inthe valve via which material of the new color is discharged for so longafter a change of color in the melt generator until even the lastcontaminants have been taken along. This is more counter-productive thanhelpful with respect to the aforesaid objective of reducing start-uplosses and of decreasing expensive material waste. Finally, a multiwayrotary valve for pelletizing plant is known from DE 100 30 584 withwhose help its high molecular plastic melts can be distributed or splitup. The problems of the start-up losses are, however, also not addressedin this reference.

With a customary design of an underwater pelletizing plant, the start-uplosses which occur and the corresponding material loss are definitelycost intensive. In particular with polymers or plastics sensitive tofreezing, e.g. products with a high crystallite melting point, it isnecessary to start and to operate at a minimal throughput of more than10 kg/h per nozzle bore. After the actual starting process, thesubsequent throughput increase is unproblematic as a rule. However,material losses arise due to the starting process itself due to start-upproduct in block form on the floor which can easily amount to severalkilograms. This is not only uneconomical because the expensive rawmaterials are transferred in a non-sellable form, but is also unpleasantfor the operator of a corresponding production plant since the blockscan turn out relatively large and have to be reduced to small particlesin an expensive process and finally have to be disposed of. Such a hotmelting block having temperatures of, optionally, more than 250° C., anddischarged via the bypass outlet of the diverter valve not least alsorepresents a potential safety risk. The problems of the discharge ofplastic melt via the bypass outlet does not only occur in the actualstart-up of a corresponding production plant for a new production job,but also when, for whatever different reasons, the plant has to beoperated out of the throughput window of the pelletizing head, inparticular when the melt volume flow has to be operated below the lowercapacity limit of the respective pelletizer head. Here, too, thediverter valve sometimes has to be switched into the bypass position sothat corresponding material waste arises.

It is therefore the underlying object of the present invention toprovide an improved pelletizing method as well as a diverter valve ofthe named kind which avoids disadvantages of the prior art and furtherdevelops it in an advantageous manner. Preferably, a ramping up of thepelletizing should be achieved with start-up losses which are as low aspossible and also an operation should be achieved which is as continuousas possible without intermediate interruptions of the process andrestart-up losses.

This object is solved in accordance with the invention by a method inaccordance with claim 1 as well as an apparatus in accordance with claim10 and a diverter valve in accordance with claim 30. Preferredconfigurations of the invention are the subject of the dependent claims.

The present invention therefore starts from the idea of using aplurality of pelletizing heads with different passage capacities and ofhereby enlarging the throughput windows to be able to work largelycontinuously without intermediate interruptions and to shortenunavoidable start-up processes by switching in pelletizing heads havingsmall throughput capacities or to minimize them with respect to thestart-up products which occur. In accordance with an aspect of thepresent invention, a plurality of pelletizing heads having differentthroughput capacities are used sequentially for the start-up of thepelletizing process, with the melt first being supplied to a firstpelletizing head having a smaller throughput capacity and then the meltvolume flow being increased and the diverter valve being switched oversuch that the melt is diverted by the diverter valve to a secondpelletizing head having a larger throughput capacity. The time and thusthe amount of the start-up product until the melt generator reaches thelower throughput limit of the pelletizing head and the pelletizingprocess can be started are cut by the use of initially one pelletizinghead having a throughput capacity which is as low as possible. Nofurther start-up product is incurred from the start onwards of thepelletizing process at the lower throughput limit of the said firstpelletizing head. The melt volume flow is increased quantitatively forso long until the diverter valve can be switched to the secondpelletizing head having the larger throughput capacity with no start-upproduct being incurred during this time period. Moreover, the throughputwindow is enlarged in total so that the number of unavoidable start-upprocedures with start-up product arising therein is reduced since it ispossible, on a ramping down of the melting performance below the lowerthroughput limit of the larger pelletizing head which may becomenecessary for various reasons, to switch back to the first pelletizinghead.

In a technical apparatus respect, it is proposed in accordance with anaspect of the present invention that the pelletizing apparatus of theinitially named kind has a control apparatus for the control of theswitching gate of the diverter valve in dependence on the melt volumeflow of the melt generator. The diverter valve can be switched to thepelletizing head having the smaller passage capacity with a small meltvolume flow by means of this control apparatus, whereas the divertervalve is switched to the second pelletizing head having the largerthroughput capacity with a larger melt volume flow. A considerableincrease in efficiency can already be achieved by such a controlapparatus, independently of the aforesaid start-up process, in that thethroughput window of the apparatus is enlarged and it is possible towork over a larger operating range without interruptions so that fewerstart-up processes become necessary. In this connection, the controlapparatus can generally realize different degrees of automation, forexample, be configured semi-automatically such that it emits anindication on the reaching of a melt volume flow which permits anoperation of the second pelletizing head having the larger throughputcapacity, said indication drawing the attention of a plant operatorthereto and such that, after a corresponding input by the plantoperator, the diverter valve then switching in the aforesaid manner tothe second pelletizing head having the larger throughput capacity sothat the melt flow is diverted from the first pelletizing head to thesecond pelletizing head. The control apparatus can also be configured tobe fully automatic in a particularly advantageous manner such that itautomatically switches the diverter valve to the respectively matchingpelletizing head on the determination of a corresponding melt volumeflow.

In a further development of the invention, the control apparatus can inparticular have control means which switch the diverter valve to thefirst pelletizing head having a smaller throughput capacity when themelt volume flow is below a lower capacity limit of the secondpelletizing head having a larger throughput capacity, but above a lowercapacity limit of the first pelletizing head and which switch thediverter valve to the second pelletizing head when the melt volume flowis above the lower capacity limit of the second pelletizing limit andstill below a lower capacity limit of an optionally present thirdpelletizing head having an even larger throughput capacity.

The control apparatus can advantageously also have volume flow controlmeans for the control of the volume flow which is directed into thediverter valve by the melt generator. Generally, in this process,different melt producers with variable volume flow can be used; forexample, the melt flow can then be generated via a corresponding screwextruder and simultaneously be varied with respect to its volume.Optionally, however, a gear pump can also be interposed between the meltgenerator and the diverter valve to control the volume flow accordingly.To be able to adapt the process in as variable a manner as possible todifferent conditions, the control apparatus is advantageously configuredsuch that it can vary, preferably continuously vary, the volume flow,also within the capacity limits of a pelletizing head.

The melt volume flow can in particular be continuously increased withinthe throughput capacity limits of the first pelletizing head on thestart-up of the pelletizing process on the pelletizing with the firstpelletizing head having a smaller throughput capacity, i.e. still beforethe switching over of the diverter valve to the second pelletizing head.Since pelletizing is already taking place with the first pelletizinghead, no start-up product is incurred, with the plant being movedcontinuously to the pelletizing process having the second, largerpelletizing head due to the increase of the melt volume flow.

The diverter valve is advantageously only switched over to the secondpelletizer head when the melt volume flow has been increased up to thelower capacity limit of the second pelletizing head and/or the uppercapacity limit of the first pelletizing head.

Generally, the diverter valve can be switched to the first pelletizinghead on the start-up of the pelletizing plant from its bypass positionin which start-up product is directed to the floor or to a suitablestorage container when the minimal conditions for a successful starthave been reached. The diverter valve can in particular be switched fromthe start-up position to the first pelletizing head in a furtherdevelopment of the invention in dependence on the melt viscosity, on themass temperature, on the mass pressure, the degassing state and/or thereaching of the required minimal volume flow. Corresponding means forthe determination can advantageously be provided in a technicalapparatus respect, preferably sensors for the detection of the saidparameters, so that the control apparatus can switch the diverter valveaccordingly in dependence on the corresponding signals. Instead ofcorresponding sensors, the said parameters can also be estimated. Inaddition to the said parameters, even further parameters such as thecolor, filler induction or further melt parameters or pelletizingparameters can be taken into account for the switching over of thediverter valve to the first pelletizing head.

In a similar manner, the switching over of the diverter valve from thefirst pelletizing head to the second pelletizing head or from the nthpelletizing head to the n+1th pelletizing head can also take place notonly in dependence on the reaching of the required minimal volume flowfor the second or n+1th pelletizing head, but alternatively oradditionally thereto in dependence on further parameters. The divertervalve can in particular be switched from the first pelletizing head tothe second pelletizing head in dependence on the pellet size, the meltmass pressure, the mass temperature of the melt or further parameterssuch as the pellet shape, surface tackiness, agglomeration, occurrenceof double grains, crystallization effects, etc. If, for example, nofurther upward latitude is given on the reaching of the maximallypossible pelletizer speed in the first pelletizing head, so that thecorrect pellet size can only be maintained or can only be reached againby switching over to the next pelletizer, the diverter valve can beswitched over to the larger pelletizing head. Alternatively oradditionally, this switchover can be carried out when the mass pressureof the melt rises above a corresponding limit value. When throughputperformances are increased, the head pressure usually also increases,which can be restrictive with some products since damage due to shearingbased on the pressure can occur. As a consequence thereof, the masstemperature of the melt can also increase too pronouncedly, wherebysimilar consequences occur. A switchover can also be a remedy here. Whenthe pellet shape is taken into account, a critical deformation of thepellets which arises on the increase of the volume flow per bore cane.g. be used as the criterion. A switchover to the larger pelletizinghead can also help here in dependence on the sensitivity of the materialproduced and on the demands on the pellet quality. Other secondaryswitchover necessities can moreover be derived from the pellet sizewhich are, however, ultimately correlated with the grain size of thepellets, namely the surface tackiness, the agglomeration, double-grain,different crystallization effects based on a different size andtemperature of the pellets and the like.

To achieve a throughput window, and thus operating window, which is aswide as possible with as few pelletizing heads as possible, butsimultaneously to ensure a switchover of the melt processing which is asfree of problems as possible from the one pelletizing head to the otherpelletizing head, the pelletizing heads connected to the diverter valvehave mutually complementary throughput capacity ranges, preferablythroughput capacity ranges seamlessly adjoining one another. Optionally,the capacity ranges could also overlap, with it, however, neverthelessapplying overall for the increase of the throughput window that thethroughput capacity region defined by both pelletizing heads is largerthan that of only one pelletizing head. A maximal utilization of eachcapacity range can be achieved by a configuration of the pelletizingheads such that their capacity ranges seamlessly adjoin one another. Forexample, when the pelletizing apparatus is configured for thepelletizing for PET, a first pelletizing head having a throughputperformance span from 2500 kg/h up to 4500 kg/h, a second pelletizinghead having a throughput capacity of 4500 kg/h up to 7500 kg/h and athird pelletizing head having a throughput capacity of 7500 kg/h up to12,500 kg/h can be used. It is understood that the capacity limits canbe selected differently, with them advantageously seamlesslycomplementing one another in a corresponding manner, however.

Generally, the pelletizing heads can be configured for differentpelletizing processes. In accordance with an advantageous embodiment ofthe invention, the pelletizing heads can form underwater pelletizingheads. Alternatively, the pelletizing heads can also form extrusionpelletizing heads or water ring pelletizing heads.

In an advantageous further development of the invention, all thepelletizing heads are of the same type, for example underwaterpelletizing heads.

In an alternative configuration of the invention, however, thepelletizing heads can also realize different pelletizing types; forexample, the pelletizing head having a smaller throughput capacity canbe an underwater pelletizing head, whereas the pelletizing head having alarger throughput performance is an extrusion pelletizing head.

The diverter valve is advantageously configured such that a diversion ofthe melt flow from one pelletizing head to the next pelletizing head ismade possible which is as rapid and as free of interruption as possible.

The bidirectionally operable diverter valve for different process stagespreferably has different flow paths for the melt so that the divertervalve for a first process stage can be operated with a first flow pathand can selectively be operated for a second process stage via a secondflow path. It can selectively output the melt via a first or a secondpelletizer connection. The respective other, not operated, flow path orpelletizer connection can simultaneously be cleaned for production viathe flow path in operation so that down times occurring hereby areomitted. The flow path or pelletizer connection not in operationnevertheless remains at temperature since the heat introduced by themelt naturally also heats up the non-operated part of the divertervalve.

In accordance with an advantageous embodiment of the present invention,the diverter valve can largely realize the plurality of production pathsstarting from only one melt generator connection. In accordance withthis embodiment of the invention, the diverter valve has, in addition tothe first pelletizer connection, a second pelletizer connection whichcan be connected to the same melt producer connection as the firstpelletizer connection. To be able to allow the melt flow to bedischarged selectively via the first pelletizer connection or the secondpelletizer connection, the diverter valve has a switching gate whichconnects the melt generator connection to the first pelletizerconnection in a first production position and connects the said meltgenerator connection to the second pelletizer connection in a secondproduction position.

The polymer melt can hereby quickly be diverted to one of the two nozzlegeometries installed at the pelletizer connections. The respective othernozzle geometry is so-to-say in stand-by and is not used. A switchoverbetween the two possible production devices can be carried out inseconds by actuation of the switching gate.

In a further development of the invention, a diverter gate can beprovided in the melt passage selectively connecting the melt producerconnection to one of the two pelletizer connections, said diverter gateswitching the melt passage through to the respective pelletizerconnection in its production position, whereas it diverts the melt flowin its start-up position and gives it to a bypass opening.

The aforesaid switching gate for the switchover between the productiondirections and the diverter gate for the start-up process can generallybe made separate from one another. In a further development of theinvention, however, they are coupled to one another, are in particularformed by a common valve body and are actuable by a common valveactuator.

In a further development of the invention, the diverter valve can alsohave a third or a further pelletizer connection, which can be connectedto the melt passage, in addition to the first and second pelletizerconnections. In this connection, the switching gate is preferablyconfigured such that it connects the third pelletizer connection to themelt generator connection in a third production position. Accordingly,the diverter valve can even switch over between more than two productiondirections.

In accordance with an aspect of the present invention, the divertervalve has a second production path made completely separate from thefirst production path. In addition to the first melt generatorconnection, to the first pelletizer connection and to the first meltpassage for the connection of the said first melt generator connectionand the pelletizer connection, the valve in accordance with thisembodiment has a second pelletizer connection as well as a second meltgenerator connection which can be connected to one another by a secondmelt passage. In this option, the change from a first production processto a second production process can advantageously take placeparticularly fast in that the initially used melt connection andpelletizer connection are released by means of quick-closing couplingsand the diverter valve with the second melt connection and pelletizerconnection and corresponding quick-couplings is again installed betweenthe melt generator and the pelletizer after a minimal mechanicalconversion and a corresponding rotation of the diverter valve itself.The second melt passage is in the cleaned state, on the one hand, and isalready pre-heated by the preceding production process, on the otherhand, so that the new production process can be started quickly.

In this connection, a diverter gate is provided in the said first meltpassage and in the said second melt passage and switches through therespective melt passage in a production position so that the melt flowcan flow from the inlet opening of the respective melt generatorconnection to the outlet opening of the associated pelletizer connectionand diverts the melt flow in a start-up position, i.e. blocks therespective pelletizer connection and directs the melt flow to a bypassopening so that the start-up procedure can take place in a manner knownper se for the new production process.

In this connection, the diverter gate of the first melt passage and thediverter gate of the second melt passage are advantageously realized ina common valve member and can be actuated by a common valve actuator.Only a control mimicry is hereby required for the switchover from thestart-up position to the production position of both production paths.The corresponding components such as the valve actuator, the controlelectronics, etc. can be dispensed with respect to the use of twoseparate diverter valves so that this solution is characterized by itscost efficiency.

Switch-through passages both for the first melt passage and for thesecond melt passage and corresponding bypass passages are provided inthe valve member for the diversion of the melt flow of the first meltpassage and of the melt flow of the second melt passage to a bypassopening in each case.

The diverter gates formed by the valve member are advantageouslyconfigured such that both diverter gates are simultaneously in theirproduction position and simultaneously in their start-up position. Whenboth production paths of the diverter valve are used simultaneously, thecorresponding production processes can hereby be started upsimultaneously. If only one of the two production paths of the divertervalve is used, the non-used production path is open in a throughgoingmanner so that it can be cleaned completely while the other productionpath is being used.

The invention will be explained in more detail in the following withreference to preferred embodiments and to associated drawings. There areshown in the drawings:

FIG. 1: a perspective overall view of a diverter valve having two meltgenerator connections with corresponding inlet openings and twopelletizer connections with corresponding outlet openings;

FIG. 2: a side view of the diverter valve of FIG. 1 which shows a planview of one of the melt generator connections;

FIG. 3: a side view of the diverter valve of FIG. 1 which shows a planview of one of the pelletizer connections;

FIG. 4: a section along the line C-C in FIG. 3;

FIG. 5: a section along the line D-D in FIG. 2;

FIG. 6: a section along the line B-B in FIG. 2;

FIG. 7: a section along the line A-A in FIG. 3;

FIGS. 8 to FIG. 13; side views and sectional views of the diverter valveof FIG. 1 corresponding to the FIGS. 2 to 7, with the diverter valve inFIGS. 8 to 13 not being shown with its diverter gate in the productionposition, but is shown in the bypass position or start-up position inwhich the melt is not yet being directed to the pelletizer connections,but to the floor;

FIG. 14: a side view of a diverter valve having two pelletizerconnections, but only one melt generator connection, with the side viewshowing a plan view of one of the two pelletizer connections;

FIG. 15: a section along the line A-A in FIG. 14 which shows thediverter gate and switching gate of the valve in its bypass position inwhich the melt generator connection is connected to neither of the twopelletizer connections, but to a bypass opening;

FIG. 16: a section of the diverter valve of FIG. 14 similar to FIG. 15,but with the switching gate and diverter gate being shown in a firstproduction position in which the melt generator connection is connectedto a first pelletizer connection;

FIG. 17: a section of the diverter valve of FIG. 14 similar to the FIGS.15 and 16, but with the switching gate and diverter gate being shown ina second production position in which the melt generator connection isin communication with the second pelletizer connection;

FIG. 18: a schematic representation of an underwater pelletizingapparatus having a diverter valve in accordance with FIGS. 14 to 17 towhich two pelletizing heads having different throughput capacities areconnected;

FIG. 19: a sectionally enlarged representation of the diverter valve ofthe pelletizer apparatus of FIG. 18, with the start-up position of thevalve being shown in the view a) and one of the two. productionpositions of the diverter valve being showing in the representation b);

FIG. 20: a schematic representation of the melt flows and pelletizationcapacities settable by the diverter valve from the preceding Figures;and

FIG. 21: a schematic representation of a diverter valve in accordancewith an alternative embodiment of the invention in which threepelletizing heads having respectively different throughput capacitiesare connected so that the melt entering into the inlet of the divertervalve can be selectively directed to one of the three pelletizing headsor to a bypass line.

The diverter valve 1 shown in FIG. 1 has a valve housing 2 at whoseouter side a first melt generator connection 3 as well as a second meltgenerator connection 4 as well as furthermore a first pelletizerconnection 5 and a second pelletizer connection 6 are provided. As FIG.1 shows, the connections 3 to 6 are distributed over the periphery ofthe valve housing 4 and are arranged on respective oppositely disposedsides. The first melt generator connection 3 is disposed opposite thefirst pelletizer connection 5, whereas the second melt generatorconnection 4 is disposed opposite the second pelletizer connection 6.

The melt generator connection and the pelletizer connection can bebrought into flow communication with one another. For this purpose, afirst melt passage 7 (cf. FIGS. 1 and 5) is provided in the interior ofthe valve housing 2 through which the first melt generator connection 3can be connected to the first pelletizer connection 5 and a second meltpassage 8 (cf. FIGS. 4 and 6) is provided through which the second meltgenerator connection 4 can be connected to the second pelletizerconnection 6. The melt passages 7 and 8 communicate in this connectionwith corresponding inlet openings 10 and 11 at the two melt generatorconnections 3 and 4 and to corresponding outlet openings 12 and 13 atthe pelletizer connections 5 and 6.

The two melt passages 7 and 8 having the respective associated firstmelt generator connection and pelletizer connection 3 and 5 or thesecond melt generator connection and pelletizer connection 4 and 6 formmutually independent and separately operable production directions. Theflow path for the melt through the one melt passage has no overlap withthe flow path through the second melt passage. The two melt passages areonly linked to one another to the extent that a common diverter valve isprovided for both melt passages, as will still be explained. As FIGS. 1,2 and 3 show, the matching first melt generator connection andpelletizer connection 3 and 5 together with the first melt passage 7connecting them vertically offset with respect to the likewise matchingsecond melt generator connection and pelletizer connection 4 and 6 andthe associated second melt passage 8. The first melt passage 7 betweenthe first melt generator connection and pelletizer connection 3 and 5extends above the second melt passage 8 between the second meltgenerator connection and pelletizer connection 4 and 6 and beyond them.It is understood that other arrangements are also possible here, e.g.the four connections 3-6 could generally be arranged at the samevertical level and the melt passages could, for example, extend beyondone another by an arcuate extension. The embodiments shown in theFigures are, however, characterized by their simple manufacturingcapability based on the straight extent of the melt passages 7 and 8.

In the interior of the valve housing or valve body 2, a diverter gate 14is provided which is associated with the two melt passages 7 and 8 andcan divert the melt flow in each of the melt passages 7 and 8 to abypass opening for the start-up process. The diverter gate 14 in thedrawn embodiment comprises a substantially cylindrical valve gate 15which is longitudinally displaceably received in a valve bore whichextends vertically in the drawn embodiment and which extendstransversely to the longitudinal axes of the melt passages 7 and 8. Itis understood that the valve gate 15 could optionally also be configuredas a rotary slide which is not actuated by axial longitudinaldisplacement, but by rotation around its longitudinal axis. Furthervalve principles are possible.

As FIGS. 1 to 5 show, the valve gate 15 is actuated by a valve actuator16 which is arranged on the upper side of the valve housing 2 and iscontrolled by an electronic control unit 17. The valve actuator 16 canrealize different operative principles, e.g. work electromagnetically orhydraulically or pneumatically. It effects the adjustment of the valvegate 15 between its production position and its start-up position orbypass position.

In the production position shown in FIGS. 5 to 7 of the valve gate 15,it switches through the two melt passages 7 and 8, i.e. the melt flowentering at the respective inlet openings 10 and 11 at the meltgenerator connections 3 and 4 is directed through the melt passages 7and 8 beyond the valve gate 15 to the associated outlet openings 12 and13 of the pelletizer connections 5 and 6. As FIGS. 4 to 7 show, the meltpassages 7 and 8 each open onto the valve bore into which the valve gate15 is inserted. Two production passages 18 and 19 are provided in thevalve gate 15 and continue the melt passages 7 and 8 so-to-say in theposition of the valve gate 16 shown in FIGS. 5 to 7.

If the valve gate 15 is moved with the help of the valve actuator 16from the production position shown in FIGS. 5 to 7 into the start-upposition shown in FIGS. 8 to 13, the valve gate 15 blocks thecommunication of the inlet openings 10 and 11 at the melt generatorconnections 3 and 4 with the outlet openings 12 and 13 at the pelletizerconnections 5 and 6. The valve gate 15 diverts the melt flow entering atthe inlet opening 10 and/or at the inlet opening 11 to a bypass openingso that the melt flow is directed to the floor on start-up. For thispurpose, the valve gate 15 has to bypass passages 20 and 21 which are inflow communication with the melt passages 7 and 8, more precisely withtheir sections originating from the inlet openings 10 and 11 in thestart-up position of the valve gate 15 shown in FIGS. 9 to 14 andso-to-say pick up the melt flow coming from there. At the other end, thetwo bypass passages 20 and 21 open into bypass outlet openings in theend face of the valve gage 15 whose lower end face is in communicationwith the outer side of the valve housing 2.

In particular two use possibilities present themselves for the divertervalve 1 shown in FIGS. 1 to 13. On the one hand, the diverter valve 1can be used with in each case only one of the melt generator connections3 and 4 and with only one of the pelletizer connections 5 and 6 at adefined point in time. That is, only one of the two productiondirections is used, whereas the other production direction, i.e. theother pair of melt generator and pelletizer connections remains unusedand is kept so-to-say on stand-by. If the correspondingly runningproduction process should be interrupted and a new production processstarted, the diverter valve is released from the respective meltgenerator and pelletizer via quick-closing couplings. The valve isrotated through 90° and then installed at the melt generator and at thepelletizer for the production process to be started using the previouslyunused melt generator connection and pelletizer connection. This newproduction process can be started in a manner known per se in that firstthe diverter gate 14 is moved to its start-up position in accordancewith FIGS. 8 to 13 so that the melt drops to the floor during thestart-up procedure. Once the plant has been started up, the divertergate 14 is moved into its production position in accordance with FIGS. 2to 7 so that the new melt flow is guided from the pelletizer beyond thediverter gate to the connected pelletizer. The changeover times arehereby minimized. Time is above all saved for the cleaning of thediverter valve. The cleaning of the previously used production passagecan take place after the valve with the fresh production passage hasbeen connected and the new production process is already running. It ismoreover advantageous that the diverter valve is already at leastapproximately at operating temperature since it was still heated fromthe previously interrupted production process.

On the other hand, the diverter valve 1 described above also providesthe option of using both production passages simultaneously, i.e. ofconnecting both melt generator connections 3 and 4 to one or more meltgenerators and equally to connect the two pelletizer connections 5 and 6to two pelletizers simultaneously.

The previously described configuration of the diverter gate 14 ensuresin this process that initially both production passages are switched tothe start-up position, i.e. both processes can be started up. A soon asboth processes have started up, the diverter gate 14 can be switchedover to start both production processes.

Independently of whether the production processes are operatedsequentially or simultaneously, the diverter gate 1 advantageouslyprovides the opportunity of operating two production processes which arethe same or also which are completely different. For instance,pelletizing processes which are the same in each case such as extrusionpelletizing or underwater pelletization can be operated via the firstmelt generator connection and pelletizer connection 3 and 5 and via thesecond melt generator connection and pelletizer connection 4 and 6, butalso different pelletizing processes can be operated, i.e. extrusionprocessing on the one and underwater pelletization on the other. In thisrespect, the respectively required nozzle plates can be used which caneither have the same section geometry and number of bores, the samesection geometry and a different number of bores, a different sectiongeometry and the same number of bores or both a different sectiongeometry and a different number of bores or which can also realize oneof these possible combinations in different constructional sizes.

The second embodiment of the diverter valve 1 in accordance with FIGS.14 to 17 substantially differs from the previously described firstembodiment in that the diverter valve has, instead of two melt generatorconnections, only one melt generator connection 3 which can beselectively connected to the first pelletizer connection 5 or the secondpelletizer connection 6 or which can be connected to the bypass openingin the start-up position of the valve. To the extent that the divertervalve 1 in accordance with FIGS. 14 to 17 agrees with the previouslydescribed embodiment, the same components are provided with the samereference numerals and reference is made to this extent to the previousdescription.

As FIGS. 14 and 15 show, in this embodiment, the melt generatorconnection 3 and the two pelletizer connections 5 and 6 are arranged atthe same level (cf. FIG. 14) and are in communication with onerespective melt passage 7, 7 a and 7 b which extend in each caseradially inwardly from the inlet opening 10 or the outlet openings 12and 13 and all three open in the valve bore in which the valve gate 15is received. The valve gate 15 of the diverter gate 14 is axiallyadjustable in the previously described manner. It includes twoproduction passages 18 and 19 (cf. FIGS. 16 and 17). In the firstproduction position of the valve gate 15, which FIG. 16 shows, thediverter gate 14 switches the inlet opening 10 of the melt generatorconnection 3 through to the outlet opening 12 of the first pelletizerconnection 5. The first production passage 18 continues the melt passage7 coming from the melt generator connection 3 to the section 7 a of themelt passage in communication with the first pelletizer connection 5 sothat the melt flow entering via the inlet opening 10 moves to thepelletizer installed at the first pelletizer connection 5.

If the valve gate 15 moves into its second production position, whichFIG. 17 shows, the diverter gate 14 switches the first melt generatorconnection 3 to the second pelletizer connection 6. The secondproduction passage 19 in the valve gate 15 continues the melt passage 7coming from the inlet opening 10 to the section 7 b of the melt passagein communication with the second pelletizer connection 6 so that themelt flow entering via the inlet opening 10 can move to the pelletizerwhich is connected to the second pelletizer connection 6.

Furthermore, the valve gate 15 can be moved into a start-up position ora bypass position, which FIG. 15 shows. In this position, the valve gate15 blocks both pelletizer connections 5 and 6 and directs the melt flowentering via the inlet opening 10 via the bypass passage 20 formed inthe valve gate 15 to a bypass opening which is provided at the end faceat the lower end of the valve gate 15. The melt can be directed to thefloor in the previously described manner via this bypass opening on thestart-up of the plant.

In this second embodiment of the diverter valve 1, in each case only oneof the two outlet openings 12 and 13 are therefore served via a commoninlet at a defined point in time. The polymer melt entering via theinlet opening 10 is diverted to one of the pelletizer connections,whereas the respective other is in stand-by and is therefore not used.The switchover can take place in a matter of seconds by actuation of thediverter gate 14.

In simple processes, the diverter gate 14 could also only have its twoproduction positions and could dispense with the bypass position and thecorresponding bypass passage 20. In this process, the so-called start-upproduct could then be reshaped to pellets on the then smallerpelletizer, whereby the otherwise usually large start-up positions wouldbe completely dispensed with.

In particular the second embodiment of the diverter valve 1 can be usedwhere complex plant should be operated with units which are as small aspossible and in very restricted space. The switchover possibility duringoperation makes it possible to avoid interruptions to a very largeextent or to realize a very wide throughput processing window on oneproduction machine by a clever selection of the two pelletizer heads.

Two pelletizing processes which are the same, that is, for example,extrusion pelletization at both pelletizer connections 5 and 6 or alsounderwater pelletization processes at both connections, can also beoperated in this embodiment of the diverter gate 1 via the twopelletizer connections 5 and 6. However, different pelletizationprocesses can also be operated, e.g. extrusion pelletization at the onepelletizer connection and an underwater pelletization at the otherpelletizer connection. In any case, nozzle plates can be used at the twopelletizer connections 5 and 6 which have the same section geometry andnumber of bores, the same section geometry with a different number ofbores, a different section geometry with the same number of bores or adifferent number of bores. It is understood that nozzle plates indifferent construction sizes can also be used with each of thesepossibilities.

Interesting use possibilities in particular result when differentpelletizer construction sizes are used at the two pelletizer connections5 and 6. The volume flow window achievable with a machine can thus e.g.be considerably increased by different nozzle plates. The loss quantityper start-up process can moreover be considerably reduced, whereby lessmaterial loss arises overall which then has to be disposed of ortreated, on the one hand, and a faster start is achieved, on the otherhand, which means less personnel and less handling overall.

The described diverter valve 1 in accordance with FIGS. 14 to 17 is usedin a particularly advantageous manner in an underwater apparatus 23 asis shown in FIG. 18, with pelletizer heads 24 and 25 having differentthroughput capacities advantageously being connected to the twopelletizer connections 5 and 6. As FIG. 18 shows, the melt suppliedhorizontally via an extruder 26 and/or via a gear pump 27 is pressed viathe diverter valve 1 through the radially arranged bores of the nozzleplate 28 of one of the two pelletizing heads 24 or 25. The strands arecut directly to pellets on discharge from the said nozzle plate 28 inthe completely flooded cutting chamber and are transported away by thewater flow 29, with the melt solidifying abruptly due to the hightemperature difference to the process water so that the spherical shapeof the pellets characteristic for underwater pelletization arises independence on the viscosity. As FIG. 18 illustrates, the pellet/watermixture exiting the cutting chamber of the respective pelletizing head24 or 25 is supplied by means of a transport line 30 to an agglomeratecollector 31 which is positioned upstream of a centrifugal drier 32.

When the plant is started up, the diverter gate 1, as first shown inFIG. 19 a, is moved into its bypass position so that the melt flow isdiverted to the floor. The melt volume flow is continuously increased bya central control apparatus 33 by a corresponding control of theextruder 26 and/or of the gear pump 28 until a lower capacity limit ofthe first pelletizing head 24 having the smaller throughput capacity isreached. As already mentioned, it is in particular necessary withpolymers sensitive to freezing, e.g. with products having a highcrystallite melting point, to start and to operate at a minimumthroughput of, for example, more than 10 kg/h per nozzle bore. It isalso necessary to ramp up apparatus components, including the divertervalve 1, to a predetermined minimum temperature which can be materialdependent.

As soon as the lower capacity limit of the named first pelletizing head24 has been reached and/or further operating parameters characteristicfor the plant or characteristic for the material have been reached, thecontrol apparatus 33 controls the diverter valve 1 such that the valvegate 15 is moved into its first production position in which the melt isdirected to the first pelletizing head 24. FIG. 20 illustrates thissmaller melt volume flow on the first pelletizing head 24 by the arrowA.

As soon as the pelletization through the first pelletizing head 24 hasstarted up, the melt volume flow is further increased until the lowercapacity limit of the second pelletizing head 25 has been reached whichis above the lower capacity limit of the first pelletizing head 24 andis advantageously approximately in the range of the upper capacity limitof the said first pelletizing head 24. The capacity ranges of the namedtwo pelletizing heads 24 and 25 preferably adjoin one another seamlesslyor a slight overlap can be provided. Once the melt volume flow has beenramped up to the said lower capacity limit of the second pelletizinghead 25, the control apparatus 33 controls the valve gate 15 into itssecond production position so that the volume flow is diverted from thefirst pelletizing head 24 to the second pelletizing head 25 in a matterof seconds.

Substantial increases in efficiency can be achieved and start-up lossescan be avoided by the start-up of the pelletization process of thesecond, larger pelletizing head 25 with interposition of the pelletizingprocess via the first, smaller pelletizing head 24.

The economic advantage should be illustrated by the following examples:

EXAMPLE 1

A pelletization for PP compounds starting from a double screw extruderhaving e.g. 150 bores in the nozzle plate and an assumed volume flowwindow of 10 kg/h and bore up to 35 kg/h and bore normally processesbetween 1,500 kg/h and up to 5,250 kg/h. In this process, the cuttingspeed of the pelletizer is necessarily feedback tracked by the factor of3.5; one starts at 1,500 kg/h and 1,030 l/min of a given bladecombination and increases the blade speed in linear fashion to 3,600l/min for 5,250 kg/h. The pellets generated in this manner then eachhave the same weight. If a 2nd pelletizing head were now installed atthis given machine having, for example, 45 bores and the resultingcapacity from 450-1,575 kg/h, the production window increases toapproximately factor 12. The same machine could thus generate from450-5,250 kg/h of high-quality pellets.

When the worst-case scenario is taken into account (approximately 3minutes start-up requirement up to the actual start with a minimumrequired throughput performance), this means for the above case:

With a standard diverter valve:

3 minutes×1,500 kg/h=75 kg material losses, per start-up process.

With a bidirectional diverter valve, this would mean:

3 minutes×450 kg/h=22.5 kg material losses, per start-up process.

There is in addition the fact that the same production machine whichrequires 3 minutes for the manufacture of 1,500 kg, will reach the 450kg/h substantially faster. This can in turn reduce the start-up time toa third, which then means in sum:

54 seconds×450 kg/h=6.75 kg material losses, per start-up process

As documented in this example, this option of the invention thereforeopens up a reduction of the loss quantity per start-up process by afactor 11.11. For the production facility, this means that, on the onehand, less material loss arises which then has to be disposed of ortreated and, on the other hand, a faster start is permitted, which meansless personnel and less handling overall (plastics have to be sucked upand cooled on discharge from the diverter valve to the bottom=floor,which naturally directly influences the operating costs).

With only one product change per day and raw material prices of

1.20/kg, this means that

81.90 can be saved per day; this is an annual savings potential of

29,839.50 p.a.

EXAMPLE 2

A pelletization for PET starting from a reactor having e.g. 250 bores inthe nozzle plate and an assumed volume flow window of 30 kg/h and boreup to 50 kg/h and bore normally processes between 7,500 kg/h and up to12,500 kg/h. In this process, the cutting speed of the pelletizer isnecessarily feedback tracked by the factor of 1.67; one starts at 7,500kg/h and 1,796 l/min of a given blade combination and increases theblade speed in linear fashion to 3,000 l/min for 12,500 kg/h. Thepellets generated in this manner then each have the same weight. If a2nd pelletizing head were now installed at this given machine having,for example, 150 bores and the resulting capacity from 4,500-7,500 kg/h,the production window increases to approximately factor 2.78. The samemachine could thus generate from 4,500-12,500 kg/h of high-qualitypellets.

When the worst-case scenario is taken into account (approximately 2minutes start-up requirement up to the actual start with a minimumrequired throughput performance), this means for the above case:

With a standard diverter valve:

2 minutes×7,500 kg/h=250 kg material losses, per start-up process.

With a bidirectional diverter valve, this would mean:

2 minutes×4,500 kg/h=150 kg material losses, per start-up process.

There is in addition the fact that the same production machine whichrequires 2 minutes for the manufacture of 7,500 kg, will reach the 4,500kg/h substantially faster. This can in turn reduce the start-up time,which then means in sum: 72 seconds×4,500 kg/h=90 kg material losses,per start-up process

As documented in this example, this option of the invention thereforeopens up a reduction of the loss quantity per start-up process by afactor 2.78. For the production facility, this means that, on the onehand, less material loss arises which then has to be disposed of ortreated and, on the other hand, a faster start is permitted, which meansless personnel and less handling overall (plastics have to be sucked upand cooled on discharge from the diverter valve to the bottom=floor,which naturally directly influences the operating costs).

EXAMPLE 3

A pelletization for PET starting from a reactor having e.g. 250 bores inthe nozzle plate and an assumed volume flow window of 30 kg/h and boreup to 50 kg/h and bore normally processes between 7,500 kg/h and up to12,500 kg/h. In this process, the cutting speed of the pelletizer isnecessarily feedback tracked by the factor of 1.67; one starts at 7,500kg/h and 1,796 l/min of a given blade combination and increases theblade speed in linear fashion to 3,000 l/min for 12,500 kg/h. Thepellets generated in this manner then each have the same weight. If a2nd pelletizing head were now installed at this given machine having,for example, 150 bores and the resulting capacity from 4,500-7,500 kg/h,the production window increases to approximately factor 2.78. The samemachine could thus generate from 4,500-12,500 kg/h of high-qualitypellets. If one were now to use the option of a multidirectionaldiverter valve and to install a further third nozzle plate/pelletizinghead combination, as shown in FIG. 21, this has the consequence of afurther reduction of the minimum start-up performance. If one e.g. takesa third nozzle with 90 bores, a throughput performance range from 2,700kg/h up to 4,500 kg/h is obtained. The pelletizing device is thusultimately available in the range from 2,700-12,500 kg/h. The productionwindow thus increases to approximately factor 4.63.

Analogously to the aforesaid, it applies to this case: when theworst-case scenario is taken into account (approximately 2 minutesstart-up requirement up to the actual start with a minimum requiredthroughput performance), this means for the above case:

With a standard diverter valve:

2 minutes×7,500 kg/h=250 kg material losses, per start-up process.

With a bidirectional diverter valve, this would mean:

2 minutes×2,700 kg/h=90 kg material losses, per start-up process.

There is in addition the fact that the same production machine whichrequires 2 minutes for the manufacture of 7,500 kg, will reach the 2,700kg/h substantially faster. This can in turn reduce the start-up time byhalf, which then means in sum:

43.2 seconds×2,700 kg/h=32.4 kg material losses, per start-up process

As documented in this example, this option of the invention thereforeopens up a reduction of the loss quantity per start-up process by afactor 7.72. For the production facility, this means that, on the onehand, less material loss arises which then has to be disposed of ortreated and, on the other hand, a faster start is permitted, which meansless personnel and less handling overall (plastics have to be sucked upand cooled on discharge from the diverter valve to the bottom=floor,which naturally directly influences the operating costs).

For a fully continuous pelletization, this means that a total of

216.12 per week can be saved with one product change per week and rawmaterial prices of

1.20/kg. this is an annual savings potential of

13,578.24 p.a.

For a discontinuous pelletization, this means that with only one productchange per day (=50 tonnes preparation with 20 h reaction time and 4 hpelletization discharge time) and raw material prices of

1.20/kg, a total of

261.12/day can be saved. this is an annual savings potential of

95,308.80 p.a.

Even if the use of the diverter valve 1 in an underwater pelletizationapparatus is described above, corresponding advantages can also beachieved with other pelletizing processes, for instance e.g. withextrusion pelletization or water ring pelletization, with optionallyalso the pelletizing heads with the different throughput capacitiesbeing able to use such different pelletizing processes.

The product flows A and B (cf. FIG. 20) can differ for the option in thefollowing application examples:

Both flows each use the same pelletization method (extrusionpelletization/extrusion pelletization; water ring pelletization/waterring pelletization; underwater pelletization/underwater pelletization)while using the respectively required nozzle plates which are either ofthe same geometry in section and of the same number of bores or are ofthe same geometry in section and of a different number of bores or areof a different geometry in section and of the same number of bores, ofare of different geometry in section or of the same number of bores orhave one of the preceding options, but can be associated with arespectively different construction size.

Both flows each use a different pelletization process (extrusionpelletization/water ring pelletization or underwater pelletization;water ring pelletization/extrusion pelletization or underwaterpelletization; underwater pelletization/water ring pelletization orextrusion pelletization) while using the respectively required nozzleplates which are either of the same geometry in section and of the samenumber of bores or are of the same geometry in section and of adifferent number of bores or are of a different geometry in section andof the same number of bores, of are of different geometry in section orof the same number of bores or have one of the preceding options, butcan be associated with a respectively different construction size.

The preferred process of them all is the underwaterpelletization/underwater pelletization use variant since in this processthe processing window which is largest overall is made available at theproduction side.

1. A method for the pelletization of plastics and/or polymers, wherein amelt coming from a melt generator (26, 27) is supplied via a divertervalve (1) having different operating positions to a plurality ofpelletizing heads (24, 25, 34) through which the melt is pelletized,characterized in that pelletizing heads (24, 25, 34) having differentthroughput capacities are used sequentially for the start-up of thepelletizing process, wherein the melt is first supplied to a firstpelletizing head (24) having a smaller throughput capacity and then themelt volume flow is increased, the diverter valve (1) is switched overand the melt is diverted by the diverter valve (1) to the secondpelletizing head (25) having a larger throughput capacity.
 2. A methodin accordance with claim 1, wherein the volume flow is increased withinthe throughput capacity limits of the first pelletizing head (24) beforethe switchover of the diverter valve (1) to the second pelletizing head(25).
 3. A method in accordance with claim 1, wherein the melt volumeflow is first maintained in the range of a lower capacity limit of thefirst pelletizing head (24) and is then increased up to the uppercapacity limit of the first pelletizing head (24) and/or up to the lowercapacity limit of the second pelletizing head (25).
 4. A method inaccordance with claim 1, wherein the diverter valve (1) is only switchedover to the second □alletizing head (25) when the melt volume flow hasbeen increased up to the lower capacity limit of the second □alletizinghead (25) and/or the upper capacity limit of the first □alletizing head(24).
 5. A method in accordance with claim 1, wherein pelletizing heads(24, 25, 34) having mutually complementary and/or overlapping throughputcapacity ranges are used.
 6. A method in accordance with claim 1,wherein the melt is diverted past the pelletizing heads (24, 25, 34) bythe diverter valve (1) in its bypass position before the supply of themelt to the first pelletizing head (24), wherein the melt volume flow isincreased until it has reached the lower capacity limit of the firstpelletizing head (24) having the smallest throughput capacity, andwherein the diverter valve (1) is then switched from its bypass positionto the first pelletizing head (24) and the melt is diverted to the firstpelletizing head.
 7. A method in accordance with claim 1, wherein thediverter valve (1) is switched from its bypass position to the firstpelletizing head (24) in dependence on at least one parameter from thegroup of melt viscosity, mass temperature of the melt and mass pressureof the melt.
 8. A method in accordance with claim 1, wherein thediverter valve (1) is switched from its bypass position to the firstpelletizing head (24) in dependence on at least one parameter from thegroup of color of the melt, filler induction and degassing state.
 9. Amethod in accordance with claim 1, wherein the diverter gate (1) isswitched from the first pelletizing head (24) to the second pelletizinghead (25) and/or from the second pelletizing head (25) to a furtherpelletizing head (34) in dependence on at least one parameter from thegroup of pellet size, mass pressure of the melt, mass temperature of themelt and pellet shape.
 10. A pelletizing apparatus for the pelletizingof plastics and/or polymers comprising a diverter valve (1) having atleast one melt generator connection (3), at least two pelletizerconnections (5, 6) as well as a switching gate (15) for the connectionof the melt generator connection (3) selectively to at least one of thepelletizer connections (5, 6), with a respective pelletizing head (24,25, 34) being connected to the at least two pelletizer connections (5,6) and a melt generator (26, 27) having a variable melt volume flowbeing connected to the melt generator connection (3), characterized inthat the at least two pelletizing heads (24, 25, 34) having differentthroughput capacities and a control apparatus (33) is provided for theswitchover of the connection of the melt generator connection (3) of thediverter valve (1) from one of the pelletizing heads (24) to another ofthe pelletizing heads (25) in dependence on the melt volume flow of themelt generator (26, 27).
 11. A pelletizer apparatus in accordance withclaim 10, wherein the control apparatus (33) has control means whichswitches the diverter valve (1) to a first pelletizing head (24) havinga smaller throughput capacity when the melt volume flow is below a lowercapacity limit of a second pelletizing head (25) having a largerthroughput capacity and/or above a lower capacity limit of the firstpelletizing head and the diverter valve switches to the secondpelletizing head (25) when the melt volume flow is above the lowercapacity limit of the second pelletizing head (25) and/or below a lowercapacity limit of a third pelletizing head (34) having an even largerthroughput capacity.
 12. A pelletizer apparatus in accordance with claim1, wherein the control apparatus (33) has start-up control means which,in a first step, move the switching gate (15) of the diverter valve (1)into a first operating position in which the melt is directed to a firstpelletizing head (24) having a minimum throughput capacity and operatesthe melt generator (26, 27) to a volume flow which is in the range ofthe lower capacity limit of the first pelletizing head (24) which then,in a second step, increase the volume flow of the melt generator (26,27) up to an upper capacity limit of the first pelletizing head (24)and/or to a lower capacity limit of the second pelletizing head (25)having a larger throughput capacity, and which finally, in a third step,operate the switching gate (15) of the diverter valve (1) into a secondoperating position in which the melt is directed to the secondpelletizing head (25).
 13. A pelletizer apparatus in accordance withclaim 12, wherein the start-up control means are configured such thatthe switching gate (15) is kept before the said first step in a bypassposition in which the melt directed into the diverter valve (1) isdirected past all pelletizing heads (25, 25, 34) until the melt volumeflow is operated in the range of the lower capacity limit of the firstpelletizing head having a minimum throughput capacity.
 14. A pelletizerapparatus in accordance with claim 1, wherein the at least twopelletizing heads (24, 25, 34) have mutually complementary throughputcapacity ranges.
 15. A pelletizer apparatus in accordance with claim 14,wherein the at least two pelletizing heads (24, 25, 34) have throughputcapacity ranges adjoining one another seamlessly.
 16. A pelletizerapparatus in accordance with claim 1, wherein detection means areprovided for the detection of the melt volume flow directed into thediverter valve (1) and the control apparatus (33) automatically switchesover the diverter valve (1) in dependence on a signal of the detectionmeans.
 17. A pelletizer apparatus in accordance with claim 1, wherein atleast one of the pelletizing heads (24, 25, 34) forms an underwaterpelletizing head.
 18. A pelletizer apparatus in accordance with claim17, wherein all the pelletizing heads (24, 25, 34) form underwaterpelletizing heads.
 19. A pelletizer apparatus in accordance with claim1, wherein at least one of the pelletizing heads (24, 25, 34) forms anextrusion pelletizing head and/or a water ring pelletizing head.
 20. Apelletizer apparatus in accordance with claim 1, wherein at least one ofthe pelletizing heads (24, 25, 34) forms an underwater pelletizing headand at least one other of the pelletizing heads (24, 25, 34) forms anextrusion pelletizing head and/or a water ring pelletizing head.
 21. Apelletizer apparatus in accordance with claim 1, wherein the divertervalve (1) is provided with a melt generator connection (3), a firstpelletizer connection (5), a melt passage (7, 8) for the communicationof the melt generator connection (3) with the first pelletizerconnection (5) as well as a second pelletizer connection (6) which canlikewise be connected to the melt passage (7), with a switching gate(14) being provided in the melt passage (7) which, in a first productionposition, connects the melt generator connection (3) to the firstpelletizer connection (5) and, in a second production position, connectsthe melt generator connection (3) to the second pelletizer connection(6).
 22. A pelletizer apparatus in accordance with claim 21, wherein adiverter gate (14) is provided in the melt passage (7) which releasesthe connection of the melt generator connection (3) to the first and/orsecond pelletizer connections (5, 6) in a production position and blocksthe first and/or second pelletizer connections (5, 6) from communicationwith the melt generator connection (3) and connects the melt generatorconnection (3) to a bypass opening (22) in a start-up position.
 23. Apelletizer apparatus in accordance with claim 22, wherein the divertergate (14) and the switching gate (14) are coupled to one another, are inparticular integrated in a common valve body (15) and can be actuated bya common valve actuator (16).
 24. A pelletizer apparatus in accordancewith claim 21, wherein a third pelletizer connection (34) is providedwhich can be connected to the melt passage (7) and the switching gate(14) is configured such that it connects the melt generator connection(3) to the third pelletizer connection (34) in a third productionposition.
 25. A pelletizer apparatus in accordance with claim 23,wherein the diverter gate or switching gate (14) is formed by acylindrical valve body which has a plurality of separate productionpassages (18, 19) and is longitudinally displaceably supported in avalve recess, in particular a valve bore.
 26. A pelletizer apparatus inaccordance with claim 25, wherein the valve body (15) has at least onebypass passage (20, 21).
 27. A pelletizer apparatus in accordance withclaim 25, wherein the valve body (15) is movably supported in adirection transverse to the connections between the melt generatorconnection and the pelletizer connection.
 28. A pelletizer apparatus inaccordance with claim 1, wherein the melt generator connections and thepelletizer connections (3, 4, 5, 6) are configured such that they can beconnected to the melt generator or to the respective pelletizer head byquick-closing couplings.
 29. A pelletizer apparatus in accordance withclaim 1, wherein means for determination, in particular sensors for thedetection of the melt viscosity, of the mass temperature of the melt, ofthe mass pressure of the melt, of the volume flow of the melt, of thedegassing state, of the pellet size and/or of the pellet shape areprovided, and wherein the control apparatus (33) switches the divertervalve (1) in dependence on at least one signal of the said detectionmeans.
 30. A diverter valve for a pelletizing apparatus comprising afirst melt generator connection (3), a first pelletizer connection (5)and a first melt passage (7) for the connection of the melt generatorconnection to the pelletizer connection, a second pelletizer connection(6), a second melt generator connection (4) as well as a second meltpassage (8) for the connection of the second melt generator connection(4) to the second pelletizer connection (6) as well as a valve body forthe control of the passage of at least one melt passage (7, 8),characterized in that the two melt passages (7, 8) are configuredseparately from one another and free of overlap; and in that the valvebody (15) in a valve recess which is in communication with both meltpassages (7, 8) and with a bypass valve (7, 8) can be moved to and frobetween a first operating position in which the first melt generatorconnection (3) is switched through to the first pelletizer connection(5) and the second melt generator connection (4) is switched through tothe second pelletizer connection (6) and a second operating position inwhich the first melt generator connection (3) and/or the second meltgenerator connection (4) is/are switched through to the bypass passage.31. A diverter valve in accordance with claim 30, wherein the valve body(15) forms a valve gate which is axially displaceably seated in thevalve recess, with the valve recess extending transversely to the meltpassages (7, 8).
 32. A diverter valve in accordance with claim 1,wherein the valve body (15) is movably supported in a directiontransversely to the connections between the melt generator connectionand the pelletizer connection.
 33. A diverter valve in accordance withclaim 1, wherein the melt generator connections and the pelletizerconnections (3, 4, 5, 6) are configured such that they can be connectedto the melt generator and/or to the respective pelletizer head byquick-closing couplings.